Direct control fuel valve for fuel flow injecting circuit

ABSTRACT

A fuel valve for a fuel flow injection circuit, operating on electrical energy rather than hydraulic energy. The fuel valve has a valve body, a first fuel inlet opening, and a distribution assembly having a plug rotating in a bushing, the plug and bushing each having an opening slit. The valve body includes a fuel outlet opening section made by an overlapping area between the opening in the bushing and the opening in the plug. A plug position unit is provided to control a position of the plug in rotation, and the plug position unit is disposed in the valve body. The valve body further contains an electric motor that drives a rotation of a reduction gear assembly, the reduction gear assembly comprising an input shaft and an output pinion. The plug comprises a toothed sector engaging on the splines of the reduction gear assembly output pinion such that rotating the electric motor causes a rotation of the plug.

DESCRIPTION

1. Field of the Invention

The invention is related to fuel valves for a fuel flow injectioncircuit into a turbojet, or more generally into an aircraft engine. Thevalve is intended to be inserted in a servocontrol loop controlling thefuel flow directed towards the injectors of an aircraft engine.

2. Prior Art

Fuel valves are well known in the state of the art, and enable to adjustthe section of the fuel passage and consequently to adjust the flowtowards the engines. For example, this type of valve is known in patentFR 2 747 174 deposited by the SAMM (Société d'Application des MachinesMotrices—Driving Machines Application Company) for a hydraulicdistributor for aircraft servocontrol. A distributor of the valve typedescribed in this patent comprises a plug mounted free to rotate insidea fixed bushing housed in a body in which an annular element is insertedbetween the plug and the bushing. The plug comprises an opening whichmore or less coincides with an opening in the bushing in which the plugis free to rotate. Rotating the plug controls the section of the fuelpassage and therefore the fuel flow. In valves controlled by anelectrohydraulically servocontrolled delivery pump, the plug is rotatedby a hydraulic regulation system in which the regulation fluid iscomposed of pressurized fuel.

The advantages of this type of fuel valve are well known, andparticularly there is no longer any need to demonstrate its reliabilityconsidering the number of years during which it has been in use.However, there are disadvantages of valves regulated by a fuel poweredelectrohydraulically servocontrolled delivery pump, particularly becausemore fuel is necessary at the pump to supply regulation control devices,particularly due to the fact that regulation control devices mustoperate when the flow is at its lowest level. This oversizing of thepump and the weight of the fuel and regulation devices are expensive interms of weight.

These devices may become seized if the fuel is polluted, which increasesthe risk of failures. To avoid the risk of the fuel freezing inregulation devices when the aircraft is at a high altitude, the fuelmust be heated before it is allowed to enter the regulation devices. Ifthe pump is oversized to maintain a satisfactory flow for regulationdevices, the heat exchanger heating the fuel must be sized accordinglywhich increases the weight. The valve cannot be tested unless the valveis pressurized, which means that the aircraft engines are started up.Finally, when the valve is replaced, special care is necessary in theworkshop to prevent foreign bodies from entering the valve, which inpractice means that the valve cannot be quickly replaced on line.

Patent application FR 72 32411 deposited on Sep. 13, 1972 with apriority claim over application U.S. Pat. No. 208,249 on Dec. 15, 1971describes a valve with a spherical closer 20. This closer 20 consists ofa sphere in which a through cylinder is formed.

An engine 84 located outside the valve body 12 drives the closer 20 inrotation through a motor shaft 86, a reduction gear external to the body12 and an output pinion 78. The output pinion 78 engages on a toothedsector 60 connected to the closer. The path of the liquid passingthrough the valve follows a trajectory along a line located in a planeperpendicular to the axis of rotation of the closer. The outside of thevalve is sealed by seals 26, 28 and a Teflon add-on part 30.

It is well known that a seal cannot be made between two parts that movewith respect to each other unless pressure is applied to the mobilepart, which requires a greater torque on the mobile part.

BRIEF DESCRIPTION OF THE INVENTION

The valve according to the invention operates on electrical energyrather than hydraulic energy.

Consequently, there is no longer any risk of pollution of the fuelcausing failures, nor is there any need for heating of the fuel whichreduces the exchanger weight and globally improves the reliability ofthe device according to the invention. Eliminating fuel as the drivervector can reduce the weight necessary for the function performed by thevalve regulation devices and therefore the weight of the turbojet isreduced. A reduction in the weight is also achieved by the smaller sizeof the pumping systems in the turbojet fuel circuits. As mentionedabove, this size depends on the flow necessary to activate the hydraulicsubassemblies when the turbojet is in operation at very low speed andtherefore when the pump outputs low flows. Therefore, the lack of anyflow necessary to actuate the valve according to the invention canimprove the sizing of the pumping system, in terms of weight. Therefore,the overall weight of the turbojet is reduced. The valve according tothe invention may also be pre-adjusted so that it outputs exactly theturbojet ignition flow, or the heating flow when the jet engine has aheating system, for example for Air Force engines, even before the fuelpasses through the valve. Consequently, the performances of the turbojetin terms of capacity and ignition speed are very much improved. Thevalve according to the invention may be tested without the input of anyhydraulic energy, which means that it can be tested without the need toturn the turbojet. Therefore, maintenance of the turbojet is very muchimproved. Finally, as mentioned above, the valve according to theinvention can be replaced and tested without the need to start up thejet, so that the valve according to the invention becomes a linereplaceable element.

In summary, a valve according to the invention has better availabilityin use and in service, is safer and more reliable, has lower maintenanceand ownership costs, improved maintenance, improved performances, andfurthermore the weight of the valve control function is lower and it ismore compact.

According to the invention, the valve is controlled using an electricmotor assembly and a mechanical reduction gear with a large reductionratio, the electric motor output shaft being input to one end of thereduction gear with the output of the reduction gear controlling theposition of a distributor plug through a gear system, and the saiddistributor. In summary, the invention relates to a fuel valve withdirect electrical control comprising:

a fuel distribution assembly comprising:

a fuel inlet opening

a bushing comprising a first opening

a mobile plug in the bushing comprising a second opening

a fuel outlet with an open section that depends on the overlapping areabetween the first opening in the bushing and the second opening in theplug

means of controlling the position of the plug in order to vary the valueof the overlapping section between the first and second openings, thevalve being characterized in that the means of controlling the plugposition comprise the following, housed in a valve body communicatingwith the distribution assembly,

a brushless electric motor rotating around a shaft AA′, this motordriving a mechanical reduction gear assembly, this assembly comprisingan input shaft and an output pinion or shaft from the reduction gearassembly, such that a motor rotation movement drives a movement of theplug and changes the overlapping areas of the first and second openings.

The fuel inlet opening is made according to a section with a fixed areaand is perpendicular to the axis of rotation of the plug. Thus, the fuelinlet is parallel to the axis of rotation of the plug. The result is anopening located on a cylindrical wall of the plug centered on the axisof the plug. Therefore, the fuel output is perpendicular to the axis ofthe plug.

Note that an opening may be composed of several holes or slits in awall. It is desirable that all holes in the plug that are combined toform the plug opening satisfy symmetry of revolution of the openingabout an axis of rotation of the plug.

The same is true for openings in the bushing. Therefore, in generalthere will be at least two openings.

Although in the following example, the motor is a rotating motor and theplug is a rotating plug, there is no reason why the motor should not bea motor with axial movement driving a plug with axial or rotatingmovement. The motor is preferably equipped with redundant stators, forbetter operating safety. The motor rotor is preferably a single-piecerotor with sides parallel to the rotor axis, for example six or eightsides with a hexagonal or octagonal section. Preferably, the motor isequipped with means of determining the angular position of the rotorabout its axis at any time, for example by magnets located on each sidein which the flux varies a signal transmitted through one or severalHall effect sensors, for example laid out axially at the same height asthe magnets.

The stator motor and the rotor housed in the valve body in communicationwith the distribution assembly is immersed in the hot pressurized fuel,which eliminates problems of sealing leaks between the plug and themotor.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and characteristics of the invention will become clearin reading the detailed description of an example embodiment of thisinvention with relation to the attached drawings in which:

FIG. 1 shows a diagrammatic description of this invention;

FIG. 2 shows a longitudinal section of an example embodiment of a valvelike that shown in FIG. 1;

FIG. 3 shows a section along line BB in FIG. 2;

FIG. 4 shows an embodiment of an opening in the bushing.

DETAILED DESCRIPTION OF AN EMBODIMENT

In the following description, elements with the same function are markedwith the same reference numbers. With reference to FIG. 1, the valveaccording to the invention is fitted with a fuel inlet 1, a bushing 2inside which a plug 3 is free to rotate in which an opening is formed,not shown in FIG. 1. The plug 3 is rotated by a mechanical reductiongear with a large reduction ratio 4. This mechanical reduction gear isitself driven in rotation by a redundant electric motor assembly 5.Redundant means that the electric motor 5 is provided with a doublestator, such that it would be possible to change over from one stator tothe other, for example in the case of a power failure or in other typesof failure. The motor 5 comprises positioning sensors 6 providinginformation about the position of the motor 5 and therefore the plug atall times. The motor 5 and reduction gear 4 assembly is housed insidethe body 7. The body 7 is provided with means not shown in FIG. 1,firstly for fixing the bushing 2 onto the body in a sealed manner, andsecondly the plug-in power supply connectors 8 for the electric motor.The plug-in connectors 8 are redundant in the sense that they areprovided with connectors necessary to supply power to the first andsecond motor stators. They also comprise the connections necessary for aprinted circuit capable of generating motor position signals that willbe mentioned later. The elements shown in FIG. 1 are shown in moredetail in FIG. 2 which is a longitudinal section through a valveaccording to the invention.

With reference to FIG. 2, the body 7 which may for example be made of alight alloy such as an aluminum alloy comprises the following componentsworking from top to bottom in an axial direction AA′ of the body 7,firstly a top end 36, an upper central part 37, a lower central part 38,and a bottom end 49. The upper central part 37 and the lower centralpart 38 house the motor 5 and the reduction gear 4 respectively.

The upper end 36 holds a bearing block support 43 made of a hard metal,for example titanium or a titanium alloy. Apart from its function as abearing block support, the bearing block support 43 cooperates with ano-ring located inside the body to form a fuel seal.

The lower end 49 of the body 7 contains the bushing 2 of thedistributor. The seal between the bushing 2 and the body 7 is made by ano-ring located in a plane perpendicular to the AA′ axis.

The seal between the body 7 and the bushing 2 refers to a seal betweenthe inside and outside of the valve body. However, there is no sealbetween the distribution assembly that comprises essentially the bushing2 and the plug 3, and the body 7 containing the reduction motorassembly. This advantageous characteristic avoids leakage problems dueto the presence of rotating seals.

As mentioned above, the motor 5 is a brushless DC motor. It comprisestwo redundant stators 9 and 10 mounted free to slide in a bore 41 in theupper central part 37 of the body 7. The stators 9 and 10 are positionedand separated from each other by a spacer 44. The spacer 44 is formedfrom an annular partition bearing on the drilling 41, which projectstowards the inside of a radial partition.

This radial partition forms the separation between the stator windings 9and 10.

The spacer 44 is held in contact axially by axial springs 34 housed atleast partly in blind holes of an intermediate bearing block support 30that will be described later. The two stators 9 and 10 are put in phasewith respect to each other by pins.

The electrical crossings to bring power from connector 8 to windings ofstators 9 and 10 are made through two sealed crossings 13 in the body 7consisting of glass beads 13 poured into through holes formed in a part46.

This part 46 is mounted in a drilling outside body 7 with an axisperpendicular to the AA′ axis. The seal is made using an O-ring 25 andthe part 46, preferably made of steel, is attached by screws.

The motor 5 also comprises a single-piece rotor 11. This rotor has eightflat sides forming an octagon, the flats of these sides being parallelto the AA′ axis. Magnets 65 forming the blades of the rotor 11 are fixedonto each of the eight sides. These magnets are preferably glued, groundand shrink fitted. They are preferably made of a rare earth, for examplesamarium cobalt to reduce the weight. The rotor shaft is centered on theAA′ axis of the body. The upper part of the shaft is shrink fitted in aball bearing 14 crimped into the bearing block support 43. Switching anddetection magnets 29 are also fixed on each of the eight flats of therotor close to the upper part of the rotor. The lower part of the shaftof the rotor 11 is shrink fitted in a ball bearing 15 crimped in theintermediate bearing block support 30. The bearings 14 and 15 of therotor shaft 11 are pressurized by means of a thrust spring 39 exertingan axial thrust on the inner rings of the bearings. This pressurereduces differential clearances and compensates for the differentialclearances originating due to temperature differences.

The motor drives the plug 3 through a reduction gear assembly 4. Thereduction gear 4 has pinions with straight teeth. It comprises threereduction stages, the first two of which are used for clearancecompensation.

In addition to the bearing 15 at the lower end of the rotor shaft, theintermediate bearing block support 30 houses bearings 45, 47 guiding theupper ends of the pinions or shafts of the reduction gear toothedwheels. The lower ends of these pinions or toothed wheel shafts areguided by bearings 54, 35 housed in a lower bearing block support 48.

At the third stage of the reduction gear, a double pinion 17 guided bybearings 47 and 35 drives a toothed sector 18 fixed to plug 3.

The elastic elements 50, 53 designed to compensate for clearance reducethe clearance between the toothed wheels or sectors forming the secondand third reduction stages, in a known manner.

The intermediate bearing block support 30 and the lower bearing support48 are aluminum parts that are housed in recesses provided for thispurpose in the lower central part 38 of the body 7. As will be describedlater, the support 48 also houses elastic stops limiting the travel ofplug 3.

All pinion guide bearings are crimped by balls in the bearing blocksupports 30 and 48.

As shown in FIG. 3, a stop 52 fixed by screws on the male splines of theplug 3 delimits the angular movement of plug 3 by coming into contact onthe elastic stops 55, 56 housed in the lower bearing support 48 andformed by a mobile pin, a retaining nut and elastic washers.

The hydraulic distribution assembly consisting of the bushing 2 and theplug 3 is screwed to the lower end 49 of the body 7 using screws 21. Theplug 3 is preferably centered by needle bearings 24 inserted between thebushing 2 and the plug 3 It is preferably held in position axially by aball thrust bearing 57 to reduce friction torque between the plug 3 andthe bushing 2. The bushing is designed to contain a receiving cavity notshown. This reception is made by a set of two outer cylindrical bearings60, 61 of bushing 2. These bearings carry O-rings 63. Preferably, thebearing 61 that penetrates furthest forwards into the connection cavityhas a smaller diameter than the bearing 60 that is located closer to thebody 7 and that is inserted last. In this way, the receiving cavity canbe assembled without any risk of damaging the O-rings 63.

The fuel is delivered by two exponentially shaped slits 23 placed on thebushing 2 symmetrically about the axis AA′ of the plug. The plug 3 hastwo triangular slits 19. The section of the fuel passage is a functionof the overlapping area of slits 19 and 23.

The shape of an exponential slit 23 in bushing 2 is shown in FIG. 4. Itis shown in the form of a graph in which the abscissa represents thevalues of the angle of rotation about the axis of the plug 3 and theordinate Y represents the values of the length of the slit measured froma plan of symmetry of the slit 23 perpendicular to the AA′ axis. Theadvantage of having an exponentially shaped opening 23 is that therelative flow error due to the positioning error can be kept constant.

Preferably, the slit is made by electro-erosion and the bushing 2 andthe plug 3 are made of stainless steel bearing steel.

The slit is said to be exponential because the distance between areference plane perpendicular to the center-line of the plug which, inthe example shown, is the plane of symmetry of the slit, and the edge ofthe slit increases exponentially with the value of the angular sector ofthe opening over most of the angular sector. In the example shown inFIG. 4, the opening 23 is exponential between 0 and 58° and is thenrectangular between 58 and 60°.

Hall effect sensors 28 located in an axial direction at the same levelas the switching and detection magnets 29 emit a signal that varies withthe relative position of the magnet 29 closest to the sensor. A set ofthree sensors 28 associated with the eight magnets 29 located on each ofthe eight faces of the rotor 11 determines twenty-four motor positions.The position of the motor is thus known to within$\frac{360{^\circ}}{24{^\circ}} = {15{{^\circ}.}}$

If the reduction ratio of the motor and the plug, N, is known, theposition of the plug is known to within $\frac{15{^\circ}}{N}.$

For example if N is between 500 and 1000, the position of the plug isknown with a precision of between 0.015 and 0.03°. The absolutepositioning precision of the plug is thus constant and depends only onthe number of positions of the motor that can be found, and thereduction ratio that is constant. Under these conditions in which theabsolute value of the plug positioning error is constant, theexponential shape of the opening means that the relative error on thefuel flow can be kept constant. The sensors 28 are placed outside thepart of the body 7 that contains fuel. They are protected by the rearbearing support 43. They are installed on a sensors printed circuit 22.

A cover 40 encloses an upper compartment of the body 7 housing the upperbearing support 43 and circuits 22 supporting the Hall effect sensors28. Another cover 42 fixed to the outside of the body 7 at the upperparts 36 and the upper central part 37 contains electrical connectionsbetween the plugs 8 and circuit pins 22 and stator windings 9 and 10.

The operation of the device according to the invention will now becommented upon.

The position of the motor 5 determines the position of the plug 3through the reduction gear 4. As described above, knowledge of theposition of the motor within 15° enables a precision of the position ofthe plug to about one hundredth of a degree, due to the large reductiongear ratio. Due to this reduction gear and the systematic use of a ballthrust bearing, friction is low and power necessary to energize thevalve is less than 5 watts.

The position information for the rotor of motor 5 is known from magnets29 and sensors 28, and is sufficient to control switching of windings ofthe stator 9 or 10 that is in service. Thus, the same sensors can beused to perform the stator winding switching function and to determinethe plug position. Consequently, these sensors are coupled to means notshown for switching the windings of the stator 9 and 10 in service, andmeans also not shown for detecting the position of the plug 3 used inthe fuel flow regulation loop.

If the motor electricity power supply is interrupted, the plug remainsin the position that it was in at the time of the cutoff. This is due tothe fact that the torque induced by reaction forces due to the deliveredfuel flow is less than the sum of the following resistance torques

dry friction torque of the reduction gear motor,

torques due to the elastic clearance compensation means 50, 53 of thereduction gear,

torque due to iron losses due to motor hysteresis.

This facility of holding the position of the plug unchanged if controlis lost is very important since loss of control does not cause anydiscontinuity in the engine feed.

Another safety aspect is due to the high motor torque available at theplug. Although the motor torque is low (of the order of a fewmillinewton.meters), a torque of 15 to 20 decanewton.meters is availableat the plug due to the large reduction ratio. This torque is sufficientto shear any metallic filings that might be introduced between thebushing and the plug. Thus, any metallic filings will not preventoperation of the valve.

Finally, since the motor is brushless, all problems due to contactbetween brushes and a collector located on the rotor are avoided. Thisthus increases the operating safety and reliability of the valve.

What is claimed is:
 1. A fuel valve with direct control, comprising: afuel distribution assembly comprising, a fuel inlet opening, a bushinghaving a first opening, a plug rotating in the bushing about an axis ofrotation of the plug, having a second opening, and a fuel outlet with anopening section that depends on an overlapping area between the firstopening in the bushing and the second opening in the plug; a plugposition unit controlling a position of the plug in order to vary avalue of an overlapping section between the first and second openings; avalve body comprising, a brushless electric motor rotating around theaxis of rotation of the plug, a mechanical reduction gear assemblydriven by the electric motor, an input shaft, and an output pinion,wherein the input shaft and the output pinion are connected to thereduction gear assembly, such that a rotation movement of the electricmotor drives a rotation movement of the plug and changes the overlappingarea of the first and second openings, and the fuel inlet openingcomprises a fixed section, perpendicular to the axis of rotation of theplug.
 2. The fuel valve according to claim 1, wherein the electric motorcomprises two switchable redundant stators.
 3. The fuel valve accordingto claim 1, wherein the electric motor comprises a single-piece rotorwith flat sides laid out along an axial direction of the single-piecerotor.
 4. The fuel valve according to claim 1, wherein the electricalmotor comprises an angular position unit configured to detect an angularposition of the electrical motor.
 5. The fuel valve according to claim4, wherein the angular position unit comprises: magnets placed on eachof the flat sides of the single-piece rotor; and Hall effect sensors. 6.The fuel valve according to claim 1, wherein the valve body furthercomprises: a top end; an upper central part; a lower central part; and alower end, wherein the top end comprises an upper bearing block supportenclosing the upper central part containing the electrical motor, andthe lower central part is housing the reduction gear assembly and thelower end into which the fuel distribution assembly fits in a sealedmanner.
 7. The fuel valve according to claim 6, wherein the upperbearing block support comprises a first bearing that guides an upper endof a shaft of the single-piece rotor of the electric motor, a lower endof the shaft of the single-piece rotor fitting into a second bearingdisposed in an intermediate bearing block support housed in the lowercentral part of the valve body.
 8. The fuel valve according to claim 7,wherein the valve body further comprises a thrust spring configured toapply axial thrust on the first and second bearings of the upper andlower ends of the shaft of the single-piece rotor of the electric motor.9. The fuel valve according to claim 7, wherein the intermediate bearingblock support comprises a set of bearings that guide an upper end of theoutput pinion and a plurality of pinions of the reduction gear assembly,a lower end of the output pinion and the plurality of pinions beingguided in a plurality of bearings disposed in a lower bearing blocksupport.
 10. The fuel valve according to claim 1, wherein the reductiongear assembly comprises clearance reduction elements.
 11. The fuel valveaccording to claim 1, wherein the plug is installed in the bushing on aset of bearings located between the bushing and the plug.
 12. The fuelvalve according to claim 1, further comprising a first and secondcylindrical bearings are disposed outside of the bushing, a firstcylindrical bearing being close to the valve body and a secondcylindrical bearing being further from the valve body, the secondcylindrical bearing having a smaller diameter than the first cylindricalbearing.
 13. The fuel valve according to claim 1, further comprising aball thrust bearing that holds the plug in contact with the bushing inthe axial direction of the single-piece rotor.
 14. The fuel valveaccording to claim 9, wherein the plug comprises a thrust bearingconfigured to prevent a contact of the plug with a plurality of stopshoused in the lower bearing block support.
 15. The fuel valve accordingto claim 1, wherein a first torque of the electric motor, having a fewmillinewton.meters, produces a second torque of 15 to 20decanewton.meters through the reduction gear assembly.
 16. The fuelvalve according to claim 4, wherein the angular position unit is coupledto a switching unit that switches the switchable redundant stators ofthe electric motor, and to the plug position unit.
 17. The fuel valveaccording to claim 1, wherein the first opening of the plug is composedof slits cutout in an outside wall of the plug, the first opening havinga symmetry of revolution about the axis of rotation of the plug.
 18. Thefuel valve according to claim 17, wherein each slit of the first openinghas an edge for which a distance between the edge and a reference planperpendicular to the axis of rotation of the plug is increasingexponentially with respect to a value of the angular rotation of theplug around the axis of rotation of the plug.
 19. The fuel valveaccording to claim 16, further comprising plug-in electrical connectors.